1. Field of the Invention
This invention relates to case formation on ferrous metals and more particularly to improved processes and apparatus therefor.
2. Brief Description of the Prior Art
It has heretofore been proposed, as described in American Society for Metals, Metals Handbook, Vol. 2, commencing at p. 677, to carburize the surface of a ferrous work piece or to carbonitriding or ion nitride the surface of the work piece to provide a case which may be hardened as the case is formed or which may subsequently be hardened.
Examples of ion nitriding by ionization in a chamber of a nitrogen containing gas are shown in the U.S. Pat. Nos. to Egan, 1,837,256, Berghaus et al., 2,837,654, Keller, 3,761,370, and Jones et al., 3,437,784 and 3,650,930.
The prior systems were particularly subject to arcing if the power input is high, which materially decreased the effectiveness of the process.
In the U.S. Pat. to Jones et al., No. 3,437,784, a power supply is shown which is intended to limit arcing by limiting the current.
None of the processes heretofore employed has proven wholly satisfactory, detrimental factors including excessive time requirements for processing because of slow heating and cooling of the work pieces, excessive power requirements, and breakdown of continuity because of arcing.